To more effectively use an ultra-thin catheter, it is generally necessary to steer the catheter through bifurcating ducts and around sharp bends within lumens of a patient's body. For many applications of a catheter that require this capability for steering the catheter, it is necessary to provide an active tip bending mechanism proximate to the distal tip of the catheter, to enable controlled deflection of the distal tip in any desired direction. The conventional approach employed in catheters uses wires for bending a segment of a metal structure at the tip of the catheter, but this approach is considered expensive for small diameter catheters and is much too expensive for single-use catheters that are intended to be discarded after being used one time with a patient. Also, the wires that are employed in this conventional approach for deflecting the distal tip at a desired angle require a relatively rigid case for support, which limits the overall flexibility of the catheter. In addition, space inside an ultra-thin catheter is sufficiently limited to preclude the use of tip bending wires.
Other types of tip bending mechanisms that have been proposed employ shape memory alloy (SMA), shape memory polymer (SMP), or electro-active polymers (EAP) as an internal actuator to bend the distal tip. Typically, as a class of actuators, shape memory materials formed as wire can change shape and/or length when their temperature is changed, which is usually accomplished by heating with an electrical current. Using a different mechanism, electro-active materials change their shape or size when stimulated directly, for example, by application of an appropriate voltage. However, there can be problems when using these types of material internally within an ultra-thin catheter to bend the tip, since the diameter of such a catheter may be too small to provide sufficient bending moment. The torque needed to bend the distal tip generally increases as the length of the moment arm decreases. The moment arm, which is the distance from the neutral axis of the catheter to a point where an actuator applies its force to bend the catheter, becomes very short if the actuator is fully contained within the protective sheathing of the catheter, which is typically less than 3 mm in diameter in ultra-thin catheters. A mechanism that relies upon axial force within the confines of a flexible shaft of a catheter can require more bending force or torque than can be provided by SMA, SMP, or EAP actuators using such a short moment arm. Accordingly, there is a need for an alternative mechanism to selectively bend the distal end of catheters, particularly of ultra-thin catheters using such materials, which is also relatively low cost and simple, and which can provide sufficient force to deflect a distal end of a small diameter catheter to enable steering the catheter around corners within a body lumen or passage. It would also be desirable to employ alternative techniques for deflecting the distal ends of a catheter that are applicable to small diameter catheters.